1. Field of the Invention
The invention relates to a semiconductor device having a gate insulating film containing a metal nitride or a metal oxynitride, a method of manufacturing the same, and a method of manufacturing a metal compound thin film including nitrogen-containing metal compound layers by atomic layer deposition.
2. Description of the Related Art
Conventionally, MOSFETs have had a gate insulating film made of a silicon oxide film which has favorable leak current characteristics and a low interface state density. Now, if a transistor having a silicon oxide film as its gate insulating film is made finer in device size, then the gate insulating film is decreased in thickness. This increases a gate leak current due to tunnel currents. When the gate leak current is increased, a substantial leak current occurs in gate-off time. There can thus occur such problems that the semiconductor device fails to make proper circuit operation, and that the power consumption increases. To solve these problems, it has recently been examined to use a high dielectric film such as a metal oxide having a high dielectric constant as the material of the gate insulating film.
Nevertheless, a metal oxide film, the high dielectric, consists of an aggregate of polycrystalline particles and thus is likely to cause impurity and metal movements through the grain boundaries. As a result, dopant impurities and metal atoms of the gate electrode can sometimes penetrate the high dielectric gate insulating film to reach the channel region, thereby impairing the device reliability.
Moreover, it has been difficult for conventional high dielectric gate insulating films to provide favorable film quality stably due to problems in the deposition processes. At present, ALD (Atomic Layer Deposition) is considered promising as a method of depositing the high dielectric gate insulating film of a transistor. It has often been the case, however, that the material itself to be used by ALD resides in the high dielectric gate insulating film as impurities, or causes a film defect. Moreover, the films constituting the high dielectric gate insulating film have sometimes deviated from their designed stoichiometric mixture ratios, failing to provide desired film properties. These phenomena will be described with reference to FIGS. 1A and 1B. FIGS. 1A and 1B are schematic diagrams showing the layer structure of a high dielectric gate insulating film that is formed by ALD. FIGS. 1A and 1B correspond to the states before and after film improvement processing by thermal annealing, respectively. Before the thermal annealing, as shown in FIG. 1A, impurities are distributed throughout the high dielectric gate insulating film. After the annealing, impurities are removed from the entire film. The film can also be densified. Nevertheless, in the lower areas of the high dielectric gate insulating film or near the substrate in particular, impurities tend to be removed insufficiently and remain intact. In addition, since metal oxides are typically prone to crystallization, the film can be partially crystallized in the annealed state of FIG. 1B. The residual impurities and the film crystallization described above may contribute to deterioration in the characteristics of the device that contains the high dielectric gate insulating film. For example, those factors can cause an increase in leak current, deviations in threshold characteristic, etc.
Japanese Laid-Open Patent Application 2002-299607 has described the configuration of introducing nitrogen into a high dielectric gate oxide film of a MIS type transistor. Specifically, the document has described a method in which a high dielectric gate oxide film is formed and then heated in an ammonia atmosphere to form a diffusion barrier layer over the film. There has also been described a method in which a silicon nitride film is formed on a high dielectric gate oxide film, followed by heat treatment so that nitrogen segregates from the interface between the high dielectric gate oxide film and the silicon nitride film (paragraphs 0043 and 0046). These methods, according to the document, can be adopted to avoid the diffusion of impurities and metal atoms from the gate electrode.
Nevertheless, the methods described in the foregoing document are to distribute nitrogen unevenly toward the top of the film, and thus will not provide any effective finding as to the method of introducing nitrogen into the entire area of the high dielectric gate insulating film in a desired distribution. The effect of suppressing impurity and metal penetration is also limited. Besides, the methods will not provide any solution to the problems described with reference to FIGS. 1A and 1B, i.e., that the crystallization of the high dielectric gate insulating film and the residual impurities can cause deterioration in transistor performance.